Preheat the oven to 300. Heat a medium-sized cast iron pot (one that has a lid) over medium heat on the stove.
Sprinkle the roast generously with salt and pepper. Add the cooking oil to the heated pot and sear the meat on all sides. Remove from the roast from the pot and set aside and reduce the heat to medium-low.
Add the onions, fennel, oregano, thyme, and garlic to the pot and sauté for about 5 minutes.
Add the beef stock, vinegar and tomato paste to the pot. Bring to a simmer and cook for another 5 minutes.
Using an immersion blender, blend the liquid until smooth and silky.
Add the chopped celery to the liquid. Then add the roast, carrots, fresh rosemary, and potatoes.
Cover with a lid and place in the 300 degree oven for 5 hours, until the meat is fork tender and falls apart.